1. Field
The disclosure relates to the field of tire manufacture and more particularly to tire building drums for assembling what are referred to as self-supporting run-flat tires.
2. Description of Related Art
The building of these tires is characterized by the fact that they comprise thick rubber profiled elements arranged in the sidewalls and generally positioned between the innerliner and the carcass reinforcing ply or plies. The purpose of these products is to withstand the load when the air pressure in the tire cover is no longer able to perform this role.
Because of this arrangement, the building of this type of tire requires special precautions to ensure a correct junction between the profiled elements and to avoid trapping air between the said profile elements, particularly when use is being made of a cylindrical drum.
This is because when laying thick profiled elements at the axial location corresponding to the sidewall region it is found that the meridian profile acting as a receiving surface for the carcass reinforcing ply is relatively uneven. This has the effect of encouraging air to become trapped between the carcass reinforcing ply and the profiled elements situated radially underneath.
Publications EP 634 266 or alternatively EP 1 847 380 disclose solutions able to solve the stated problem and described tire-building drums comprising grooves arranged on the receiving surface of the drum and axially spaced so that they can be positioned more or less in line with the zone in which the thick profiled elements are laid. In this way, by suitably determining the shape of the groove it becomes possible, after the laying of the thick profiled elements, to obtain a carcass reinforcing ply receiving surface that is substantially cylindrical. The thick profiled element hugs the profile of the said groove in such a way that its radially external surface is substantially aligned with the generally cylindrical exterior surface of the tire-building drum. The carcass reinforcing ply is laid on a cylindrical surface that is free of zones liable to trap air.
The next profiled elements are generally laid after the drum has been brought to a second laying diameter. Steps are then taken to ensure that, at the end of this first shaping, and, moreover, of the subsequent shapings, the radially external surface of the thick profiled element remains aligned with the receiving surface of the drum.
More specifically, publication EP 1 847 380 describes a drum in which, when the drum is brought to a first laying diameter, a mechanical means keeps an elastic body away from the bottom of the groove so as to align the radially external surface of the elastic body with the receiving surface of the tire-building drum.
When the drum is brought to a second laying diameter greater than the first laying diameter and the elastic body is pressed firmly against the bottom of the groove, the radially external surface of the thick profiled element forms, with the surface of the drum, a surface that is generally cylindrical.
This type of tire-building drum therefore addresses the problem of the laying of the thick profiled elements used for the manufacture of what are known as self-supporting run-flat tires entirely satisfactorily.